What's the scope height?

[Tommie]

Using ballistic software to calculate impact points at distance. Obviously scope height figures into the equation.
My dilemma:
What's the scope height when the scope is not parallel to the bore? I'm using Burris Signature XTR rings and will be dropping the front of the scope 5 MOA (or possibly raising the rear 5MOA) with inserts in this particular case but knowing that 20 MOA bases are super common I'm sure this is an issue that people already have solved. So when inputting the scope height do I enter the rear height, front height or center height. Or maybe something else?
Edit: shooting distances will be mostly between 350 and 900 yards

 

[Mark W]

I’ve always just measured from somewhere close to center of the scope. This has always worked for me getting on paper from 600-1000 yards. If my elevation needs any adjustment, I’ll play with the BC until everything matches up. After that, I can get real close at any known yardage. I’m using StrelokPro.

 

[BoydAllen]

If you want to get that picky, you can do a little trig. With a 4" ring spacing, an angle of 20 minutes (20 MOA) which is a third of a degree. would amount to a difference in ring height of .023". The back ring would be that much higher than the front.

 

[Tesoro]

I remounted the scope on my 6br yesterday and bore sighted it at 500 yds and first shot was only 2ft off target. If I had tried to calc the trajectory on the app based on 100 yd zero I would have been way farther off course on the vertical. Not sure why but I figured it was like your question regarding moa rails and not being parallel to bore. Bottom line is the value I see in the ballstics app anymore is for approximate windage adjustments. I shoot in the mountains so I can always find the right sized stump or boulder to bore sight at distance. Might not be able to do that on the average range.

 

[wildcatter]

Once I zero at 200 yards, using my scope hieght ( ceter of scope measured from center of bore, or action ) I have never been off more than a couple inches using my Ziess Hunting App. out to 600 yards. I don't care if I use a 20moa rail, or a standard picatinny rail.

I have tested this with a .125" error, and it still puts me within 2 or three 1/8 moa clicks at 600 yards. I've done this with 68 grain ppc loads as well as 108 and 95 grain 6x47L loads.

I have to enter correct coefficient and velocity measurements, but a few thousandths in my hieght entry, gets me close enough to kill ground hogs out to 600 yards. Definitely inside a 7 ring on a 600 yard score target.

So in answering your front or rear question, use the center between both rings, you will be extremely close, but coefficient and velocity I find more critical beyond 500 yards. All important, but a few thousandths in scope hieght has been less critical once I'm zero'd at 200 yards, using that for my base for more or less yardage using the Ziess App.

 

[STOMP442]

Take your measurements at the scope bell. Dia divided by 2. Barrel dia at scope bell divided by 2 then measure the gap between the bell and the top of your barrel. Add all those together and that will give you your sight height.

 

[Eagle Six]

I talked with one of the guys at Applied Ballistics about 20 MOA rails and scope height. He said the measure from the bolt center to the center of the scope tube either just in front of the turret housing or just to the rear of the turret housing. They make nor expect any compensation for bases or rails.

 

[David Conder]

I flunk trig

 

[3Ackleys]

Using Boyds measurement of .023" you will see a difference of 2" @ 1000 yards.

 

[Eagle Six]

Any minor deviation caused by a 20-30 MOA base is most likely going to be noise mixed in with the difference between real BC and the bullet manufacturers claimed BC, if that is what you are using. Sometimes, for long range ballistics calculation we need to adjust bullet velocity for shorter distances (600-700 yards) and bullet BC for longer distance (1,000+ yards), by actually shooting those distances for real results and making the necessary changes in the ballistics calculator to achieve truer solutions. If there was a 2" difference at 1,000 yards I doubt on any given day I could shoot the difference to prove it!

 

[Tesoro]

I talked with one of the guys at Applied Ballistics about 20 MOA rails and scope height. He said the measure from the bolt center to the center of the scope tube either just in front of the turret housing or just to the rear of the turret housing. They make nor expect any compensation for bases or rails.

Yeah re-thinking this...the reticle is where the turrets are so if you tilt the scope up or down 20 moa then the reticle is at the pivot point so poa and poi would not change with any significant degree. Now if the reticle was in the objective or ocular lens then that would be a different story.

 

[Eagle Six]

With most modern scope the reticle isn't in the turret housing. The turrets push on the erector lens set which bend the light which makes us think the reticle is moving. The reticle is not far from the center of the turret housing and will be a bit different between makes, models, or FFP/SFP . I think anywhere in the center section of the tube will make little difference.

 

[Tesoro]

With most modern scope the reticle isn't in the turret housing. The turrets push on the erector lens set which bend the light which makes us think the reticle is moving. The reticle is not far from the center of the turret housing and will be a bit different between makes, models, or FFP/SFP . I think anywhere in the center section of the tube will make little difference.

Yes it isn't in the turrets, thats where the gears are but the reticle is close to that area in most scopes.

 

[Rob01]

Caliper or ruler works. Get within 1/4” and you are fine. Center of windage to center of bore. Simple to measure. Amount of moa in base doesn't matter. I have used this up to 60 moa bases.

 

[Mike Casselton]

Rob has it correct and also the simplest method.
Measure from the center of the gas hole to the gap in the scope ring.

If you need to be more precise, do the same type of measurement on the rear ring and split the difference.

You can be off about a tenth of an inch and it won't really matter.